Chassis battery disconnect

Due to unknown parasitic battery loss on our ancient RV, I installed battery cut-off switches (got them from Harbor Freight) on both my chassis and house batteries. I disconnect the batteries every time I put the RV into storage after a trip.

I had hard-wired a propane detector into our RV so that would have drained the house battery over time. The parasitic load on the engine battery I did not bother to try and track down.

Could be many reasons for a difference in MPG, certainly wind speed as tatest said. Also, your driving speed. Did you use your genny? Was the tire inflation the same? Did the alternator have to do more chassis battery charging?

fortytwo wrote:
My electronic battery disconnect stopped working so I installed a knife blade switch on my battery bank. Stopped the discharging, but may have an unwanted side effect. Just completed a 900 mile trip and my mileage is almost 1 mpg less than I got on last summer's trip. May be coincidence; will require more tracking. I did have a roof coating installed but can't conceive how that would create enough additional drag to make such a difference.

1 mpg difference on a trip you made last year compared to same trip a year later may have nothing to do with engine electronics, which usually normalize from the reset within the first couple of hours of driving. I regularly see 2-3 mpg difference trip to trip, and segment to segment on a long trip, from changing driving conditions, more importantly wind speed and direction. My 8.3 mpg can drop to 6.5 into a headwind and rise to 10 or 11 with a good tailwind.

Similarly, my full size van will range from 11 mpg to 16 mpg with wind and cruising speed as factors, and will even get up to 18 mpg in the winter when not using A/C is combined with a tailwind.

From the point of view of the electronics, there should no difference between disconnecting with a switch (or pulling off the cable) versus having them lose power by running the battery down.

From the point of view of the battery, it is a whole lot better to disconnect it, so you have only self-discharge, than to let the onboard electronics drag it down to 10 volts or lower. These deep discharges greatly shorten battery life.

My electronic battery disconnect stopped working so I installed a knife blade switch on my battery bank. Stopped the discharging, but may have an unwanted side effect. Just completed a 900 mile trip and my mileage is almost 1 mpg less than I got on last summer's trip. May be coincidence; will require more tracking. I did have a roof coating installed but can't conceive how that would create enough additional drag to make such a difference.

Cruisineasy wrote:
I have a 2011 Jayco Greyhawk. Would it cause any damage to any electronics in the rig if I disconnected the the chassis battery when it is stored??

When my MH is parked at home I keep a Battery Tender hooked up to it. It keeps the battery charged and maintained. I also keep one hooked up to the house batteries but I take the negative cable off. Just keep the inter connected cables on the batteries in parallel. Works for me.

Just keep in mind that the battery connection cables remaining in the trailer will be HOT if you connect the trailer SHORE POWER cable to 120VAC or run from a generator without the batteries connected. Might be good idea to always wrap the HOT end in a plastic sandwich bag. If it shorts out on you you will have to locate some hidden fuses...

Also I would mark the HOT +12VDC connections with red tape or touch them up with RED fingernail polish. You do not want to connect them up in REVERSE ORDER as that also will blow fuses in your trailer.

I stated this with the trailer batteries in mind but same would go for the TRUCK Start battery. It is not that big of a problem with the truck start battery as they usually have a large and small size connector.

Roy Ken

I just bought a quick battery disconnect switch with the blade type, and started using it to disconnect my negative on the engine battery. the old battery was discharging once every couple of weeks. I replaced the old battery with a new one. I did the same on my old motor home. It does not harm the engine components, and is better for the battery, but I still run the engine at least once a week, but the battery can go still work weeks or months later.

No it will not cause damage, disconnect the black cable first, then the red one if you want to, when connecting the red goes first and then the black one.

If you live in a smog control area, you will need to drive the RV for at least a half an hour so that the computer regains all of the parameters of the engine, other wise it will fail, not because of smog but the lack of sufficient sampling for the computer's memory.

navegator